Perovskite-type metal oxide compounds

ABSTRACT

Perovskite-type catalyst consists essentially of a metal oxide composition is provided. The metal oxide composition is represented by the general formula A 1−x B x MO 3 , in which A is a mixture of elements originally in the form of single phase mixed lanthanides collected from bastnasite; B is a divalent or monovalent cation; M is at least one element selected from the group consisting of elements of an atomic number of from 22 to 30, 40 to 51, and 73 to 80; and x is a number defined by 0≦x&lt;0.5.

RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/797,578, filed on Feb. 7, 1997, U.S. Pat. No. 5,977,017 issued Nov.2, 1999 which in turn is a continuation-in-part of application Ser. No.08/630,603, filed on Apr. 10, 1996, U.S. Pat. No. 5,939,354 issued Aug.17, 1999 which applications are hereby incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to perovskite-type catalystswhich are useful in carbon monoxide oxidation, hydrocarbon oxidation,nitrogen oxide reduction and oxidation of trapped soot particles. Inaddition, the present invention relates to perovskite-type materialsdisplaying so-called giant magnetoresistance (GMR). Furthermore, thepresent invention relates to methods of making and using perovskite-typecatalysts and materials.

2. Description of Related Art

Perovskite compositions are nominally designated as ABO₃, in which Arepresents a rare earth metal, such as lanthanum, neodymium, cerium orthe like, and B represents a transition metal such as cobalt, iron,nickel or the like. It is known in the art that perovskite-typematerials are useful for the catalytic oxidation and reduction reactionsassociated with the control of automotive exhaust emissions. It is alsoknown that perovskite materials (powders, single crystals and thinfilms) containing Mn on the B-site show giant magnetoresistance effect(GMR), such that on application of a magnetic field, the electricalresistivity of the material drops drastically due to a field-inducedswitching of the crystal structure. For this reason, GMR has attractedconsiderable attention for device applications, such as magneticrecording heads.

Several techniques have been used to produce perovskite-type catalystmaterials for the treatment of exhaust oases from internal combustionengines. The ability of such materials to effectively treat internalcombustion exhaust gases depends on the three-way activity of thematerial, i.e., the capability for nitrogen oxide reduction, carbonmonoxide oxidation and unsaturated and saturated hydrocarbon oxidation.The following patents describe such materials and techniques in thethree-way catalytic application: U.S. Pat. Nos. 3,865,752; 3,865,923;3,884,837; 3,897,367; 3,929,670; 4,001,371; 4,049,583, 4,107,163;4,126,580; 5,318,937. In particular, Remeika in 3,865,752 describes theuse of perovskite phases incorporating Cr or Mn on the B-site of thestructure showing high catalytic activity. Lauder teaches in U.S. Pat.No. 4,049,583 (and 3,897,367) the formation of single-phase perovskitematerials showing good activity for CO oxidation and NO reduction.Tabata in U.S. Pat. No. 4,748,143 teaches the production of single-phaseperovskite oxidation catalysts where the surface atomic ratio of themixed rare earth elements and the transition metal is in the range of1.0:1.0 to 1.1:1.0. The rare-earth component can be introduced using amixed rare-earth source called “Lex 70” which has a very low Ce content.

Tabata further teaches in U.S. Pat. No. 5,185,311 the support of Pd/Feby perovskites, together with bulk ceria and alumina, as an oxidationcatalyst. The perovskite is comprised of rare earths on the A-site andtransition metals on the B-site in the ratio 1:1.

In addition to these patents there are numerous studies reported in thescientific literature relating to the fabrication and application ofperovskite-type oxide materials in the treatment of internal combustionexhaust emissions. These references include Marcilly et al., J. Am.Ceram. Soc., 53 (1970) 56; Tseung et al., J. Mater. Sci., 5 (1970) 604;Libby, Science, 171 (1971) 449; Voorhoeve et al., Science, 177 (1972)353; Voorhoeve et al., Science, 180 (1973); Johnson et al.,Thermochimica Acta, 7 (1973) 303; Voorhoeve et al., Mat. Res. Bull., 9(1974) 655; Johnson et al., Ceramic Bulletin, 55 (1976) 520; Voorhoeveet al., Science, 195 (1977) 827; Baythoun et al., J. Mat. Sci., 17(1982) 2757; Chakraborty et al., J Mat. Res., 9 (1994) 986. Much of thisliterature and the patent literature frequently mention that the A-siteof the perovskite compound can be occupied by any one of a number oflanthanide elements (e.g., Sakaguchi et al., Electrochimica Acta, 35(1990) 65). In all these cases, the preparation of the final compoundutilizes a single lanthanide, e.g., La₂O₃. Meadowcroft in Nature, 226(1970) 847, refers to the possibility of using, a mixed lanthanidesource for the preparation of a low-cost perovskite material for use inan oxygen evolution/reduction electrode. U.S. Pat. No. 4,748,143 refersto the use of an ore containing a plurality of rare-earth elements inthe form of oxides for making oxidation catalysts.

In addition to the above-mentioned techniques, other techniques havebeen developed for the production of perovskite materials containing Mnon the B-site which show giant magnetoresistance effect (GMR). Suchmaterials are generally made in the forms of powders, single crystalsand thin films. A common technique is the growth of single-crystal froma phase-pure perovskite source (see, for example, Asamitsu in Nature,373 (1995) 407). All such techniques use a phase-pure perovskitecompound with a single lanthanide on the A-site, in addition to analkaline earth dopant. An example of such phase-pure perovskitecompounds is La_(1-x)Sr_(x)MnO₃.

It is also known in the art that it is difficult and expensive toprepare individual rare-earth compounds such as individual lanthanides.The cost is high for making perovskite-type materials with a singlelanthanide on the A-site. Therefore, a need exists for using low-coststarting materials to manufacture inexpensive catalyst materials,simultaneously having high temperature stability and high three-wayactivity for use in conversion of CO, hydrocarbons and oxides ofnitrogen in modern gasoline-powered automobiles. A need also exists forthe manufacture of bulk materials, thin films and single-crystals ofmaterials showing GMR, using inexpensive starting materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide improved catalystmaterials with three-way activity, manufactured from inexpensivestarting components. It is also an object of the present invention toprovide a perovskite-type metal oxide compound having giantmagnetoresistance effect. It is further an object of the presentinvention to provide a method of making and using improved catalystmaterials and the perovskite-type metal oxide compounds of the presentinvention.

Accordingly, one object of the present invention is to provide aperovskite-type catalyst consisting essentially of a metal oxidecomposition. The metal oxide composition is represented by the generalformula A_(a-x),B_(x),MO_(b), in which A is a mixture of elementsoriginally in the form of single phase mixed lanthanides collected frombastnasite; B is a divalent or monovalent cation; M is at least oneelement selected from the group consisting of elements of an atomicnumber of from 22 to 30, 40 to 51, and 73 to 80; a is 1 or 2; b is 3when a is 1 or b is 4 when a is 2;and x is a number defined by 0≦x<0.7.

In a preferred embodiment, the single phase perovskite-type materials ofthe present invention have a formula A_(1-x)B_(x)MO₃, and preferably xis about 0 to 0.5.

In another preferred embodiment, the single phase materials of thepresent invention are perovskite-type materials having a formulaA_(2-x)B_(x)MO₄.

Another object of the present invention is to provide a perovskite-typemetal oxide compound represented by the general formulaA_(a-x)B_(x)MO_(b), in which A is a mixture of elements originally inthe form of single phase mixed lanthanides collected from bastnasite; Bis a divalent or monovalent cation; M is at least one element selectedfrom the group consisting of elements of an atomic number of from 22 to30, 40 to 51, and 73 to 80; a is 1 or 2; b is 3 when a is 1 or b is 4when a is 2; and x is a number defined by 0≦x<0.7. The perovskite-typemetal oxide compound of the present invention contains Mn on its B-site.

The present invention also provides a catalytic converter. The catalyticconverter comprises:

(a) a perovskite-type catalyst comprising a metal oxide compositionrepresented by the general formula:

A_(1-x)B_(x)MO₃

wherein

A is a mixture of elements originally in the form of a single phasemixed lanthanide collected from bastnasite:

B is a divalent or monovalent cation;

M is at least one element selected from the group consisting of elementsof an atomic number of from 22 to 30, 40 to 51, and 73 to 80;

x is a number defined by 0≦x<0.5; and

(b) a solid structure for supporting the catalyst.

In a preferred embodiment, the catalytic converter also comprises acarrier powder. The Perovskite-type catalyst may be in a bulk form or inthe form of a dispersion.

Another object of the present invention is to provide a method ofpreparing a perovskite-type catalyst consisting essentially of a metaloxide composition having component elements represented by the generalformula A_(a-x)B_(x)MO_(b), in which A is a mixture of elementsoriginally in the form of single phase mixed lanthanides collected frombastnasite; B is a divalent or monovalent cation; M is at least oneelement selected from the group consisting of elements of an atomicnumber of from 22 to 30, 40 to 51, and 73 to 80; a is I or 2; b is 3when a is 1 or b is 4 when a is 2; and x is a number defined by 0≦x<0.7.

The method comprises forming a homogeneous mixture of a single phasemixed lanthanide salt collected from bastnasite and respective salts oroxides, of elements B and M and forming a perovskite-type metal oxidecomposition from said homogeneous mixture.

A further aspect of the present invention provides a method of making acatalytic converter of the present invention. The method comprises:

(a) providing a perovskite-type catalyst comprising a metal oxidecomposition represented by the general formula:

A_(1-x)B_(x)MO₃

wherein

A is a mixture of elements originally in the form of a single phasemixed lanthanide collected from bastnasite;

B is a divalent or monovalent cation;

M is at least one element selected from the group consisting of elementsof an atomic number of from 22 to 30, 40 to 51, and 73 to 80;

x is a number defined by 0≦x<0.5;

(b) providing a support structure having a surface,

(c) forming a stable slurry suspension of the perovskite-type catalyst;and

(d) depositing the suspension of the perovskite-type catalyst on thesurface of the support.

In one embodiment of the present invention, the perovskite-type catalystmay be in a bulk form or in the form of a dispersion. A carrier powdermay be mixed with the bulk perovskite-type catalyst to form the slurrysuspension and then be deposited on the surface of the support.Alternatively a carrier powder may be used to form a perovskite-typecatalyst in the form of a dispersion.

The present invention is further defined in the appended claims and inthe following description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of the present invention and themanner of obtaining them will become more apparent, and will be bestunderstood by reference to the following description, taken inconjunction with the accompanying drawings. These drawings depict atypical embodiment of the present invention and do not therefore limitits scope. They serve to add specificity and detail in which:

FIG. 1 shows a processing route of bastnasite and its mixed lanthanidederivatives.

FIG. 2 shows the X-ray diffraction trace of a perovskite material of thepresent invention.

FIG. 3 shows the three-way catalytic activity of a perovskite materialof the present invention.

FIG. 4 shows the three-way catalyst “light off” test.

FIG. 5 shows the three-way catalytic activity of the perovskite-basedcatalyst of composition Ln_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Pd_(0.06)O₃ inan exhaust has stream.

FIG. 6 shows the three-way catalytic activity of the perovskite-basedcatalyst of composition Ln_(1.4)Sr_(0.3)Mn_(0.9)Ni_(0.04)Ru_(0.06)O₃ inan exhaust gas stream.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is based on the discovery that single phase mixedlanthanides collected from bastnasite can be used in makingperovskite-type materials. According to the present invention, singlephase mixed lanthanides from bastnasite can be used to makeperovskite-type catalysts with improved activities. The catalysts of thepresent invention have three-way activity and can be used for theremoval of unsaturated and saturated hydrocarbons, nitrogen oxides andcarbon monoxide from the exhaust gases of internal combustion enginesand from industrial waste gases. They also exhibit high thermal andchemical stability.

As discussed above, the source of the lanthanide component in prior artis an oxide, carbonate, nitrate or acetate of one lanthanide element,with a high degree of purity with respect to other lanthanides, or amixture of highly purified lanthanide elements. The perovskite materialsof the present invention overcome the disadvantage of using relativelyexpensive, research-grade Sources for the lanthanide elements. Theadvantage of the use of a mixed lanthanide source relates to the needfor an inexpensive fabrication route. The cost of producing perovskitesusing single phase mixed lanthanides of the present invention is threeto four times less expensive than the cost of using a single rare-earthelement.

Accordingly, the present invention provides a single phaseperovskite-type catalyst consisting essentially of a metal oxidecomposition represented by the general formula, A_(a-x)B_(x)MO_(b), inwhich A is a mixture of elements originally in the form of single phasemixed lanthanides collected from bastnasite; B is a divalent ormonovalent cation; M is at least one element selected from the groupconsisting of elements of an atomic number of from 22 to 30, 40 to 51,and 73 to 80; a is 1 or 2; b is 3 when a is 1 orb is 4 when a is 2; andx is a number defined by 0≦x<0.7. In a preferred embodiment, the singlephase perovskite materials of the present invention have a formulaA_(1-x)B_(x)MO₃, and preferably x is about 0 to 0.5. In anotherpreferred embodiment, the single phase materials of the presentinvention are perovskite-type materials having a formulaA_(2-x)B_(x)MO₄. In a further preferred embodiment, the single phaseperovskite materials of the present invention have the general formulaA_(a-x)B_(x)MO_(b), in which A is a mixture of elements selected fromthe group consisting of lanthanides of an atomic number of from 57 to 71or, alternatively, A is a mixture of elements selected from the groupconsisting of yttrium and lanthanides of an atomic number of from 57 to71.

A sile phase mixed lanthanide is a single compound wherein the cationpositions in the compound's crystal structure can be occupied by avariety of lanthanides. Alternatively, the cation positions of thesingle phase mixed lanthanide may be occupied by a variety oflanthanides. The single phase mixed lanthanides of the present inventionare generated from bastnasite ore. They may contain a number oflanthanide cations and nitrate carbonate or chloride anions. Thesemonophasic materials may be hydrated materials, namely 49 they maycontain waters of hydration. Thus, hydroxyl ions may take up anionpositions in the lattice of the monophasic material.

It is known in the art that bastnasite is an ore of a mixed lanthanidefluoride carbonate. The mixed lanthanide fluoride carbonates ofbastnasite adopt a crystal structure with discrete layers of [LnF] and[CO₃] (Y. Ni et al., Am. Mineral., 78 (1993) 415), wherein F can bereplaced by OH (M. Fleischer, Can. Mineral, 16 (1978) 361).

Different lanthanide (Ln) derivatives can be prepared from bastnasitethrough methods commonly known in the art. Examples of such methods aredescribed in Cer. Eng. Sc. Proc, by B. T. Kilbourn, 6 (1985) pp.1331-1341, and in The Discovery and Industrialization of the Rare Earthsby Fathi Habashi, UNOCAL 76 MOLYCORP (1994), FIG. 14, the text of whichis incorporated herein by reference. A typical flow chart relating Lnderivatives obtained from bastnasite ores is shown in FIG. 1. Accordingto FIG. 1, bastnasite ore is first treated by comminution and floatationto generate bastnasite concentrate. Through acid dissolution techniques.Ln carbonate, Ln chloride or Ln nitrate is generated from the bastnasiteconcentrate. Through roast and acid leaching techniques, soluble andinsoluble fractions are generated from the bastnasite concentrate. Laconcentrate is from the soluble fraction, and Ce concentrate is from theinsoluble fraction. Further solution extraction from the Ln concentrateproduces low-Ce (i.e., 4% CeO₂ when analyzed on an In oxide basis) andmixed Ln compounds.

Ln derivatives can be classified in terms of steps needed to producethem. Both the bastnasite concentrate and the Ln derivatives generatedby acid dissolution contain a natural ratio of Ln's. A natural ratio ofIn's is a ratio identical or close to their natural distributionproportions in bastnasite ores. A typical analysis on a Ln oxide basisis: 4.0% Pr oxide, 50.5% Ce oxide, 33.7% La oxide, and 11.8% Nd oxide.It is understood that this ratio may vary owing to inherent variability,not only in the ore body but also in the mineral itself. Both the La andCe concentrates contain a modified ratio of Ln's. A modified ratio ofLn's is a ratio different from the natural ratio of Ln's, and a ratioexisting in any by-products of the processing route of bastnasite isshown in FIG. 1.

The single phase mixed lanthanides used in the present invention may begenerated from any of the above-mentioned concentrates. They may have anatural ratio of Ln's or a modified ratio of Ln's. In general, anysingle phase mixed lanthanides generated from any of the above-mentionedconcentrates may be used as a lanthanide source for making aperovskite-type material of the present invention.

For example, Ln derivatives generated from bastnasite concentrate byacid dissolutions, such as, but not limited to, Ln chloride, Lncarbonate and Ln nitrate, are single phase, pure compounds with amixture of Ln cations, and can be used as an Ln source for the purposeof the present invention. Such Ln derivatives have a natural ratio ofLn's and are cerium-rich. Likewise, single phase mixed lanthanides, suchas, but not limited to, hydrated mixed lanthanide carbonate or hydratedmixed lanthanide nitrate may be crystallized as single phase compoundswith a mixture of 1 n cations coming out of a solution of Laconcentrate. Such single phase mixed lanthanides have a modified ratioof Ln's. For example, they may contain about ⁴% of CeO₂, when analyzedon an Ln oxide basis.

The perovskite-type materials of the present invention are doped on theA-site with sufficient and appropriate monovalent or divalent cations toform electrically conductive, monophasic perovskites with high catalyticactivity. The examples of monovalent or divalent cations include, butare not limited to, Na, K, Li, Ca, Sr, Ba, Pb and the like. The amountof monovalent or divalent cations are sufficient and appropriate if theyare in such an amount that the bulk composition's atomic ratio ofelement M in the B site and the A and B elements in the A site are about1:1.

Similarly, a sufficient and appropriate M element is used for the B siteof the perovskite or perovskite type materials of the present invention.M is one or more elements with atomic numbers lying in the range 22 to30, 40 to 51, and 73 to 80. Examples of M element include, but are notlimited to, Fe, Mn, Co, Ni, Ru, Cr, Pd, Cu and the like. The amount of Melements is sufficient and appropriate if they are in such an amountthat the bulk composition's atomic ratio of element M in the B site andthe A and B elements in the A site are in 1:1. In a preferredembodiment, the Mn element is in B-site.

The present invention also provides a method of making theperovskite-type materials of the present invention. The method comprisesthe steps of making a homogeneous mixture of single phase mixedlanthanide salts collected from bastnasite and respective salts, oroxides, of elements B and M, and forming the perovskite-type metal oxidecomposition from the homogeneous mixture.

The homogenous mixture of salts may be in a form of a solution or a formof a solid. The homogenous mixture may be formed by dissolving, a singlephase lanthanide salt, together with salts containing elements B and M,respectively, in a solution such as water and also can be formed bydissolving in acid, e.g., vitric acid. The mixture may also be formed byGrinding a single phase lanthanide salt with salts or oxides of elementsB and M. Other methods known in the art for forming the homogenousmixture may also be used. The salts used in the method of the presentinvention may be nitrates, carbonates, hydroxides, acetates, oxalates orchlorides of component elements A, B and M. Oxides of B and M may alsobe used to make the homogenous mixture. The amount of each salt used isa function of the desired composition in the final perovskite compound.

A perovskite-type metal oxide material may be formed from the mixture bytechniques such as, but not limited to, pelletizing, spray-drying,sintering or calcination. Those techniques may be used alone or incombination to obtain perovskite-type metal oxide materials.

In a preferred embodiment, a malic acid solution technique is used whenthe homogenous mixture is in a form of a solution. For example, thefollowing salts may be dissolved in a solution such as water to form ahomogenous mixture: a single phase lanthanide salt, such as, but notlimited, to single phase mixed hydrated lanthanide carbonate, singlephase mixed hydrated lanthanide nitrate or the like; a salt of elementsB, such as, but not limited to, calcium nitrate tetrahydrate, strontiumnitrate or the like: and one or more salts of element M, such as, butnot limited to, cobalt nitrate hexahydrate, hydrated manganese nitrate,hydrated chromium nitrate, hydrated iron nitrate, hydrated palladiumnitrate, nickel nitrate or the like. Then malic acid may be added anddissolved into the solution. A foam-like precipitate is formed throughheating the solution to a temperature between 190 and 310° C. in air.The foam can be heated or calcined to a temperature of 400° C. or higherto form the perovskite-type material. In a preferred embodiment, theform is calcined in a temperature at a range of 500-1100° C. in air forabout 1-25 hours. Periodic grinding during the calcining process ispreferred. Alternatively, when an additional and different element M isdesired, the salt or oxide form of such an element may be added to theprecipitate and powdered or sintered together with the precipitate toform a powder of single phase perovskite-type metal oxide materialshaving multiple M elements.

In another preferred embodiment, a sintering or calcining technique isused when the homogenous mixture is in a form of a solid. For example, asingle phase mixed lanthanide salt may be mixed with oxides of elementsB and M by grinding and homogenizing to form a homogenous mixture. Thenthe mixture can be powdered or sintered at temperatures from 700 to1000° C. to form a powder of single phase perovskite-type metal oxidematerials.

The powders of perovskite-type materials can be further formed intopellets or beads. Techniques such as uniaxial cold press and the likemay be used to form the pellets or beads.

The metal oxide materials made by the method of the present inventionhave perovskite structure and they are single phase materials. X-raydiffraction analysis is used to show the perovskite structure ofmaterials and the presence, if any, of second phases or impurity phases.The Brunauer, Emmett and Teller (B.E.T.) surface area is measured by agas absorption apparatus for proving how fine-grained the powder is. Thesurface area is measured and is normalized to the Weight of solid, i.e.,m²/g. A high m²/g (specific surface area) corresponds to a smallfundamental grain or particle size. Catalytic functions occur onsurfaces; therefore, it is important that a catalyst can be made with alarge specific surface area.

The perovskite-type material of the present invention may be in a bulkform or in the form of a dispersion, depending on the methods used tomake it. A perovskite-type material is in a bulk form if it is the onlymaterial present in the system. On the other hand, a perovskite-typematerial is in the form of a dispersion if the system contains not onlyperovskite-type material, but also carrier materials. In this form, theperovskite-type material is made up of a large number of smallperovskite particles existing on the surfaces of carrier materials(alumina, etc.).

A bulk perovskite-type material may be made by any method describedabove. The above-described methods may also be used to make aperovskite-type material in the form of a dispersion if the methodsfurther include a step of mixing or impregnating a solution of thehomogenous mixture with a carrier material. For example, in accordancewith one embodiment of the present invention, a perovskite-type catalystin the form of a dispersion may be made by the steps of: (a) forming asolution of a homogeneous mixture of single phase mixed lanthanide saltscollected from bastnasite and respective salts or oxides of elements Band M, (b) mixing or impregnating the solution with a carrier material,and (c) calcining the impregnated carrier material under a conditionthat allows perovskite-type metal oxide composition to be formed on thecarrier material.

For the purpose of the present invention, a carrier material may be aporous solid oxide that is, itself, not catalytically active. Carriermaterials are used to provide a high surface area for the dispersedphase, and one that is stable at high temperatures and in a range ofreducing and oxidizing conditions. In one embodiment of the presentinvention, carrier material is used in a powder form. Examples of acarrier material include, but are not limited to, inert powder such asgamma-alumina, any ceria-based powders (imparting oxygen storagecapacity), or any mixture of titania, silica, alumina (transition andalpha-phase), ceria, zirconia, Ce_(1-x)Zr_(x)O₂, and all the possibledoped ceria formulations.

The single phase perovskite-type metal oxide materials of the presentinvention can be used as a catalyst. The perovskite-type catalyst of thepresent invention may be used as is, or after being deposited oncarriers of various types and forms. They may take the form of pelletsand particles which may be of uniform composition. They may take asupported form with the active ingredient being dispersed through orpresent as a coating on the individual bodies.

For example, the perovskite-type material of the present invention canbe extruded or molded into monolithic bodies, including honeycombs thatconsist of channels running the length of the body with thininterconnected walls. The methods of making such extrusions are wellknown in the art. Briefly, in making the extrusions, organic compoundsand liquids are added to the perovskite-type powders such that a plasticmass of appropriate rheological properties is formed. This body isextruded through an appropriately designed die to form a green body andis then heat-treated or calcined at temperatures to impart a sufficientmechanical strength and durability and to completely remove all organicadditions.

The perovskite-type powder of the present invention also may be formedinto an open cell foam according to methods known in the art. Briefly,the ceramic powder which is to be formed into a foam is mixed withcarbon powder. The mixture is heated to high temperature in asufficiently oxygen-containing atmosphere such that the carbon supportis removed leaving a solid ceramic foam with open, interconnected cells.

In addition, the perovskite-type powder of the present invention may bedeposited or applied to the surface of a ceramic honeycomb or some othermonolith. The ceramic honeycomb may be a type of alumina, mullite,cordierite or some other alumino-silicate support. The application canoccur via a washcoat, as known in the art. Alternatively, theperovskite-type materials of the present invention may also be depositedor applied to the surface of a metal honeycomb support. Preferably, allthe supports, either metallic or ceramic, offer a three-dimensionalsupport structure.

Furthermore, the perovskite-type powder of the present invention may bedispersed on the ceramic or metallic support by impregnating the supportwith the same solution used to make the perovskite-type powder inaccordance with the present invention. Preferably, the support ispre-coated with carrier powders. The impregnated support is heated to ahigh enough temperature to allow the perovskite-type phase to form onthe surface of the carrier powders of the support in a highly dispersedstate.

One aspect of the present invention also provides a catalytic converterand a method of making a catalytic converter. For the purpose of thepresent invention, the term “catalytic converter” refers to a solidstructure having catalytic activity. The solid structure may be enclosedin a housing, i.e., a metal can. In general, the catalytic convertercomprises a structural support and a catalyst that coats the support. Acatalytic converter contains the appropriate type and amount of catalystso that it can fulfill a precise catalytic function. For example, it mayperform a conversion function. The conversion can be of gases into othergaseous products, liquids into other liquids, liquids into gaseousproducts, solids into liquids, solids into gaseous products, or anycombination of these specific conversions. In all cases, the conversionreaction or reactions are deliberate and well-defined in the context ofa particular application, i.e., simultaneous conversion of NOx, HC andCO, conversion of MTBE to carbon dioxide plus steam, etc.

In accordance with one embodiment of the present invention, a catalyticconverter of the present invention includes a perovskite-type catalystof the present invention and a structure for supporting the catalyst. Inone embodiment of the present invention, a catalytic converter may alsocontain a carrier material. The perovskite-type catalyst contained inthe converter may be in a bulk form or in the form of a dispersion. Theconverter may also contain one or more different catalysts which are inthe same form or different forms.

The converter may contain one carrier material or a mixture of differentcarrier materials. Preferably, the carrier materials are in a powderform. The carrier material may be an inert powder or any other carriermaterials that are known in the art for forming a washcoat on a support.The term “washcoat” as used herein refers to a coating of oxide solidsthat is formed onto a solid support structure. For the purpose of thepresent invention, the oxide solids may be carrier oxides or one or morecatalyst oxides or mixture of carrier oxides and catalyst oxides (i.e.,perovskite-type materials). A washcoat may be formed by forming a slurryof the oxide solids and depositing, i.e., washing, the slurry onto thesupport structure. Other methods that are known in the art for forming awashcoat on a support are also included in the present invention.Examples of a carrier material include, but are not limited to, inertpowders such as gamma-lumina, any ceria-based powders (imparting oxygenstorage capacity), or any mixture of titania, silica, alumina(transition and alpha-phase), ceria, zirconia, Ce_(1-x)Zr_(x)O₂, and allthe possible doped ceria formulations.

For the purpose of the present invention, a structure for supporting acatalyst of the present invention may be any support structures known inthe art. In one embodiment of the present invention, the structure is ahoneycomb support. The honeycomb support may be a ceramic honeycombsupport or a metal honeycomb support. In a different embodiment, thesupport structure may be in a form of beads or pellets.

In accordance with another embodiment of the present invention, acatalytic converter of the present invention may also contain anon-perovskite type catalyst, in addition to the perovskite-typecatalyst, for achieving different conversion results. For example, thenon-perovskite-type catalyst may be a base, a noble metal or a mixturethereof. Examples of a base metal catalyst include, but are not limitedto, metallic elements with atomic numbers 3-4, 11-15, 19-32, 37-43,48-52, 56-75, 80-83. Examples of a noble metal catalyst include, but arenot limited to, elements with atomic numbers 44, 45, 46, 47, 76, 77, 78and 79.

Different methods may be used to make the catalytic converters of thepresent invention. For example, in one embodiment, perovskite-typecatalysts of the present invention in bulk form may be suspended to forma stable suspension and deposited to a solid support structure bymethods known in the art. Alternatively, the bulk catalyst may be mixedwith a carrier powder or pre-mixed carrier powders, i.e., inert powderssuch as gamma-alumina, any ceria-based powders or a mixture thereof, toform a stable slurry suspension. The slurry suspension is then depositedto a solid support by a slurry deposition technique that is known in theart.

In accordance with another embodiment of the present invention, acatalytic converter of the present invention is made by depositing theperovskite-type catalyst of the present invention in the form of adispersion onto a solid support. According( to this embodiment, asolution of a homogenous mixture of salts of element A and respectivesalts or oxides of elements B and M may be mixed and impregnated into anumber of carrier powders including, but not limited to, titania,silica, alumina (transition and alpha-phase), ceria, zirconia,Ce_(1-x)Zr_(x)O₂ and all the possible doped ceria formulations. Theseimpregnated powders are dried and calcined at elevated temperatures toform perovskite-type catalysts in the form of a dispersion. The formedcatalysts may be then slurry deposited individually, in combinations, orsequentially onto commercially available support structures.Alternatively, the carrier powders may be pre-mixed, and the solutionsof the homogenous mixtures are impregnated into pre-mixed carrierpowders, such as ceria-alumina mixtures. For the purpose of the presentinvention, a solution of a homogenous mixture contains elements A, B andM in a ratio that is given by the formula A_(1-x)B_(x)M, wherein x is anumber defined by 0≦x<0.5.

In another embodiment of the present invention, one or more carrierpowders may be first slurry deposited to a solid support to form awashcoat according to methods known in the art. Then, solutions of thehomogenous mixtures of the present invention are impregnated into thepre-formed washcoat(s). After the catalyst impregnation, the supportbody is calcined in air at high temperature to form the desired phasechemistry. Examples of carrier powders that may be used to form awashcoat include, but are not limited to, titania, silica, alumina(transition and alpha-phase), ceria., zirconia, Ce_(1-x)Zr_(x)O₂, andall the possible doped ceria formulations.

In accordance with one embodiment of the present invention, the washcoatmay contain not only carrier powders, but also perovskite-type catalystsof the present invention. For example, bulk perovskite-type catalysts ofthe present invention may be mixed with carrier powders to be slurrydeposited to a solid support to form a washcoat. Then, solutions of thehomogenous mixtures may be impregnated into the washcoat and calcined toform perovskite-type metal oxides on the %washcoat. In this embodiment,the washcoat may contain the bulk perovskite-type catalyst of thepresent invention and may also contain, optionally, ceria-based oxygenstorage material and high-surface area gamma-alumina.

It is the discovery of the present invention that, not only thesolutions of the perovskite-type materials of the present invention maybe deposited into a washcoat containing a perovskite-type material,other non-perovskite-type catalysts may also be deposited to such awashcoat to achieve unexpected catalytic results. Accordingly, acatalytic converter of the present invention may also be formed bydepositing a non-perovskite-type catalyst into a washcoat of a supportwhich contains a perovskite-type material. In one embodiment of thepresent invention, the non-perovskite-type catalyst may be a base, or anoble metal, or a mixture thereof. Examples of a base metal catalystinclude, but are not limited to, metallic elements with atomic numbers3-4, 11-15, 19-32, 37-43, 48-52, 56-75, 80-83. Examples of noble metalcatalysts include, but are not limited to, elements with atomic numbers44, 45, 46, 47, 76, 77, 78 and 79.

The perovskite-type catalyst of the present invention has an improvedthree-way catalytic activity for the removal of unsaturated andsaturated hydrocarbons, nitrogen oxides and carbon monoxide from theexhaust gases of internal combustion engines, including small gasolineengines and from industrial waste gases. They also exhibit high thermaland chemical stability. Further, they possess resistance to sulfurdioxide poisoning.

Accordingly the perovskite-type catalysts of the present invention havea wide range of applications. For example, the perovskite-type catalystsof the present invention may be used for clean-up of exhaust emissionsfrom all kinds of internal combustion engines. They may also be used inindustrial catalysis for the production of industrial chemicals,fertilizers, and products in the polymer and plastics field. They mayfurther be used in all oil-derived processes and products. They may alsobe used for clean-up of industrial process emissions including., but notlimited to, volatile hydrocarbons, chlorinated hydrocarbons and MTBE.

In particular, the catalysts of the present invention may be used, forexample, in the control of gaseous and particulate emissions from alltypes of Otto cycle and Diesel cycle internal combustion engines(including Otto cycle lean-burn engines, Otto cycle and diesel cycleengines equipped with SCR capability with ammonia or hydrocarbonintake); olefin polymerization, hydrogenation reactions, methanolsynthesis from syngas (either carbon monoxide and hydrogen mixtures ormixtures also containing carbon dioxide); hydroformylation of alkenes;Fischer-Tropsch Synthesis; isomerization of hydrocarbons; aromizationreactions; catalytic cracking reactions; reactions involving the removalof Sulfur and/or Nitrogen and/or Oxygen from oil-derived hydrocarbons byhydrogenation; steam reforming of methanol and other hydrocarbons andhydrocarbon mixtures (e.g., gasoline) to produce gas mixtures containinghydrogen; the latter reactions where the hydrogen gas is used in afuel-cell; epoxidation of alkenes; partial and/or selective oxidation ofhydrocarbons; oxidation of volatile organic compounds (VOCs), includingMTBE.

It is known in the art that perovskite materials (powders, singlecrystals and thin films) containing Mn on the B-site show the giantmagnetoresistance effect. Because of this, the perovskite materials ofthe present invention having Mn on the B-site may also be used to makedevices such as magnetic recording heads or the like.

The following examples are intended to illustrate but not to limit, thescope of the invention. While the method described provides thenecessary information to make any given perovskite material of thepresent invention, typically those that might be used, other proceduresknown to those skilled in the art may alternatively be used.

METHODS OF MAKING PEROVSKITE OR PEROVSKITE-TYPE MATERIAL OF THE PRESENTINVENTION EXAMPLE 1

A single phase perovskite material of the nominal chemical compositionLn_(0.6)Ca_(0.4)CoO₃ was synthesized by dissolving 104.15 g of mixedhydrated lanthanide carbonate, Ln₂.(CO₃)_(3.) 4H₂O, in a solution formedby dissolving 57.5 g of calcium nitrate tetrahydrate, Ca(NO₃)_(2.) 4H₂Oand 177.15 g of cobalt nitrate hexahydrate, Co(NO₃)_(3.) 6H₂O, into 2liters of water. Intense stirring was used to form a solution of all thecomponents. The mixed lanthanide carbonate hydrate contains La, Ce, Prand Nd. To this solution was added 200 g of malic acid. The solution wasplaced in a rotary evaporator and heated by a water bath. The water bathwas heated to 90° C. The solution was reduced to 20% of its originalvolume and had the consistency of a thick syrup. The syrup was placedinto a flat refractory tray and heat-treated at 200° C. for 1 hr. Thesyrup was converted into a solid foam. The foam was then heat-treated ata temperature of 700° C., in air for 2 hrs. with an intermediate grindafter 1 hr. The product comprised a black powder of the noted chemicalcomposition. X-ray diffraction analysis showed the material to be asingle phase perovskite with a B.E.T. specific surface area of 13 m²/g.

The mixed hydrated lanthanide carbonate used herein is a single phasecompound crystallized from the La concentrate generated from thebastnasite ore. Therefore, it contained a modified ratio of Ln's. Thecerium concentration is about 4% on a lanthanide oxide basis.

FIG. 2 shows the measured X-ray diffraction intensity as a function oftwo-theta when a perovskite material of compositionLn_(0.6)Ca_(0.4)CoO₃, made according to Example 1, is impinged by asource of monochromatic X-ray radiation. FIG. 2 shows that the compoundof Example 1 is a single phase perovskite material. All the peaks in thetrace can be indexed according to the crystal structure of theperovskite phase.

EXAMPLE 2

A single phase perovskite material of the same chemical composition asin Example 1 was synthesized by dissolving 104.15 g of mixed hydratedlanthanide carbonate, Ln_(2.)(CO₃)_(3.) 4H₂O, in a solution formed bydissolving 57.5 g of calcium nitrate tetrahydrate, Ca(NO₃)_(2.) 4 H₂Oand 177.15 g of cobalt nitrate hexahydrate, Co(NO₃)_(3.) 6 H₂O, into 2liters of water. Intense stirring was used to form a solution of all thecomponents. To this solution was added 200 g of malic acid. The solutionwas reduced to half its volume by heating at 80° C. on a hot plate for 3hrs. The solution was then placed on a refractory tray and heated at200° C. for 1 hr. The solid foam so obtained was heat-treated at 700° C.in air for 2 hrs. with an intermediate grind after 1 hr. The productcomprised a black powder of the noted chemical composition and X-raydiffraction analysis showed the material to be a single phase perovskitewith a B.E.T. specific surface area of 13 m²/g.

EXAMPLE 3

A single phase perovskite material of the same composition as inExamples 1 and 2 was synthesized by grinding and homogenizing 52.08 g ofmixed hydrated lanthanide carbonate, 6.83 of calcium oxide, CaO and22.82 g of cobalt oxide, CoO. The mixture was heated at 800° C. for 36hrs. in air with periodic regrinding. The product, comprising a blackpowder, was characterized by X-ray diffraction as being a single phaseperoskite compound B.T.E. surface area of 1.2 m²/g.

EXAMPLE 4

A single phase perovskite powder, as produced according to Example 1,was consolidated into pellets by using a uniaxial cold press. Thepellets so produced were heat-treated at a range of heat treatmenttemperatures for a period of 1 hr. The pellets so heat-treated wereanalyzed by X-ray diffraction and the B.E.T. specific surface area wasmeasured. In each case, X-ray diffraction showed that the materialremained a single-phase perovskite material regardless of heat treatmenttemperature.

EXAMPLE 5

A single phase perovskite powder of the compositionLn_(0.83)Sr_(0.17)MnO₃ was synthesized according to the methodillustrated in Example 2. The powder was made by dissolving 105.3 g ofmixed hydrated lanthanide carbonate, Ln₂(CO₃)_(3.) 4H₂O, 10.1 g ofstrontium nitrate, Sr(NO₃)₂ and 50 g of hydrated manganese nitrate,Mn(NO₃)_(2.) 6H₂O, into 2 liters of water. Malic acid was added to thesolution and heat treatments were carried out as in Example 2. Theproduct comprised a black powder of the noted chemical composition andX-ray diffraction analysis showed the material to be a single phaseperovskite with a B.E.T. surface area of 9.3 m²/g.

EXAMPLE 6

A single-phase perovskite powder of composition Ln_(0.7)Sr_(0.3)CrO₃ wassynthesized according to the method illustrated in Example 2. A solutionwas made by dissolving 23.48 g of mixed hydrated lanthanide carbonate,Ln₂(CO₃)_(3.) 4H₂O, 7.52 g of strontium nitrate, Sr(NO₃)₂, and 45 g ofhydrated chromium nitrate, Cr(NO₃)_(3.) 9H₂O, into 1 liter of water. 60g of malic acid was added to the solution. Heat treatments were carriedout as in Example 2. A heat treatment temperature of 900° C. wasrequired to obtain a phase-pure, perovskite material. The product was anolive green powder with a B.E.T. surface area of 11.3 m²/g.

EXAMPLE 7

A single-phase perovskite powder of compositionLn_(0.6)Ca_(0.4)Fe_(0.8)Mn_(0.2)O₃ was synthesized according to themethod illustrated in Example 2. A solution was formed by dissolving47.68 g of mixed hydrated lanthanide carbonate, Ln₂(CO₃)_(3.) 4H₂O,26.50 g hydrated calcium nitrate, Ca(NO₃)_(2.) 4H₂O, 90.7 g of hydratediron nitrate, Fe(NO₃)_(3.) 9H₂O, and 17.93 g of hydrated manganesenitrate, Mn(NO₃)_(2.) 6H₂O, into 2 liters of water. To this solution wasadded 130 g of malic acid. Heat treatments were carried out as inExample 2. The product was a black, single-phase perovskite powder ofthe noted chemical composition, having a B.E.T. surface area of 32.1m²/g.

EXAMPLE 8

A single phase perovskite material of compositionLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04) _(Ru) _(0.06)O₃ was synthesized. Asolution was formed using 45.78 g of mixed hydrated lanthanidecarbonate. Ln₂(CO₃)_(3.) 4H₂O,52.18 g of manganese nitrate hexahydrate,Mn(NO₃)_(2.) 6H₂O, 8.56 g of strontium nitrate Sr(NO₃)₂, and 2.35 g ofnickel nitrate hexahydrate, Ni(NO₃).6H₂O, in 1 liter of water. To thesolution was added 60 g of malic acid. This solution was reduced to halfthe original volume by heating on a hot plate for 3 hrs. The solutionwas converted into a solid foam as in Example 2. The solid foam soobtained was heated at 350° C. for 2 hrs. and ground with 1.61 g ofruthenium oxide, RuO₂. This mixture was then heat-treated at 800° C. for10 hrs. to produce a single-phase perovskite powder of the desiredcomposition with a B.E.T. surface area of 9.8 m²/g.

EXAMPLE 9

A single-phase perovskite powder of compositionLn_(0.8)K_(0.2)Mn_(0.95)Ru_(0.05)O₃ was synthesized according to themethod illustrated in Example 8. A solution was formed by dissolving52.17 g of mixed hydrated lanthanide carbonate. Ln₂(CO₃)_(3.) 4H₂O, 4.66g of potassium nitrate, KNO₃, and 62.77 g of hydrated manganese nitrate,Mn(NO₃)_(2.) 6H₂O, in 2 liters of water. 110 g of malic acid wasdissolved in this solution. As illustrated in Example 8, RuO₂ was addedto the foamed solution after a heat treatment at 350° C. In thisexample, 1.53 g of RuO₂ was added to the ground, heat-treated foam. Thismixture was heat-treated at 700° C. for 15 hrs. to produce a black,single-phase perovskite powder of the noted composition and with aspecific, B.E.T. surface area of 10.5 m 2/g.

EXAMPLE 10

A single-phase perovskite powder of compositionLn_(0.7)Sr_(0.3)Ru_(0.05)O₃ was synthesized according to the methodillustrated in Example 8. A solution was formed by dissolving 39.27 g ofmixed hydrated lanthanide carbonate, Ln₂(CO₃)_(3.) 4H₂O, 12.57 g ofstrontium nitrate, Sr(NO₃)₂, and 75.27 g of hydrated 1 chromium nitrateCr(NO₃)₃9H₂O, in 1.5 liters of water. To this solution, 82 g of malicacid was added. 1.32 of RuO₂ was added to a powder comprising the foamedsolution that had been heat-treated at 350° C. This mixture was thenheat-treated at 1000° C. for 32 hrs. to produce a dark brownsingle-phase perovskite powder of the noted composition. The B.E.T.surface area of the powder was 12.9 m²/g.

EXAMPLE 11

A single-phase perovskite of composition LinNiO₃ was synthesizedaccording to the method illustrated in Example 2. A solution was formedby dissolving 38.97 g of mixed hydrated lanthanide concentrate,Ln₂(CO₃)_(3.) 4H₂O, and 40 g of hydrated nickel nitrate, Ni(NO₃)_(2.)6H₂O, to 0.5 liters of water. Into this solution was dissolved 50 g ofmalic acid. Heat treatments were carried out as in Example 2. The blackpowder so obtained was a single-phase perovskite of the notedcomposition, with a specific surface area of 23.2 m²/g.

EXAMPLE 12

A single-phase powder with the perovskite-type “K₂NiF₄” structure ofcomposition Ln₂(Cu_(0.6)Co_(0.2)Ni_(0.2))O₄ was synthesized according tothe method illustrated in Example 2. A solution was formed by dissolving50.0 g of mixed hydrated lanthanide concentrate, Ln₂(CO₃)_(3.) 4H₂O,12.32 g of hydrated copper nitrate, Cu(NO₃)_(2.) 6H₂O, 5.13 g ofhydrated nickel nitrate, Ni(NO₃)_(2.) 6H₂O, and 5.14 g of hydratedcobalt nitrate, Co(NO₃)_(3.) 6H₂O, in 2 liters of water. Into thissolution was dissolved 150 g of malic acid. Heat treatments were carriedout as in Example 2. The black powder so obtained was a single-phasepowder with the “K₂NiF₄” structure of the noted composition and with aspecific surface area of 14.3 m²/g.

EXAMPLE 13

A single phase perovskite material of compositionLn_(0.8)K_(0.2)Mn_(0.95)Ru_(0.05)O₃ was synthesized according to themethod illustrated in Example 9. A solution was formed by dissolving50.3 g of a mixed hydrated lanthanide nitrate, Ln(NO₃)_(3.) 4H₂O, 39.56g of hydrated manganese nitrate Mn(NO₃)_(2.) 6H₂O, and 2.94 g ofpotassium nitrate, KNO₃, in 1.5 liters of water. 51 g of citric acid wasdissolved in this solution. As illustrated in Example 9, RuO₂ was addedto the foamed solution after a heat treatment at 350° C. In this example0.96 g of RuO₂ was added to the ground, heat-treated foam. This mixturewas heat-treated at 700° C. for 15 hrs. to produce a black, single-phaseperovskite powder of the noted composition with a B.E.T. surface area of12.2 m²/g.

The hydrated lanthanide nitrate is a single phase product ofcrystallization coming out of the solution of La concentrate generatedfrom the bastnasite ore. The product has a modified ratio of Ln's. Thecerium concentration on an oxide base is about 5% of the total Ln's.

EXAMPLE 14

A single phase perovskite material of compositionLn_(0.6)Ca_(0.4)Fe_(0.8)Mn_(0.2)O₃ was synthesized according to themethod illustrated in Example 2. A solution was formed by dissolving71.64 g of Ln carbonate, Ln₂(CO₃)_(3.) 4H₂O, 39.75 g hydrated calciumnitrate, Ca(NO₃)_(2.) 4H₂O, 136.05 g of hydrated iron nitrate,Fe(NO₃)_(3.) 9H₂O, and 26.90 g of hydrated manganese nitrate,Mn(NO₃)_(2.) 6H₂O, into 3 liters of water. To this solution was added130 g of malic acid. Heat treatments were carried out as in Example 2.The product was a black, single-phase perovskite powder of the notedchemical composition, having a B.E.T. surface area of 34.3 m²/g. Themixed hydrated Ln carbonate used in this example is a single phasecompound from bastnasite concentration by acid dissolution process. Ithas a natural ratio of Ln's. Therefore, the cerium concentrationreflects the natural ratio of cerium in any given bastnasite, i.e., itis slightly higher than the La content on a LnO basis.

EXAMPLE 15

A single-phase perovskite materialLi_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Pd_(0.06)O₃ was synthesized bydissolving 50.0 g of mixed hydrated lanthanide carbonate Ln₂(CO₃)_(3.)4H₂O, in a solution formed by dissolving 60.57 g of hydrated manganesenitrate, Mn(NO₃)_(2.) 6H₂O, 9.92 g strontium nitrate, Sr(NO₃), 3.67 ghydrated palladium nitrate, Pd(NO₃).xH₂O (where x is about 1.7), and2.73 g nickel nitrate. Ni(NO₃).6 H₂O, into 1 liter of water. The mixedLn compound contains La, Ce, Pr and Nd and is derived from bastnasite.To the solution that was formed, 194.0 g of malic acid was added anddissolved. This solution was dried at 190-310° C. for 1 hr. andheat-treated in a temperature range 500-1100° C. in air for 1-25 hrs.The product from any of these heat treatments was found to be asingle-phase perovskite powder. The surface area varied depending on theprecise heat treatment. The B.E.T. specific surface area was 8.2 m²/g ifthe heat treatment was 1000° C. for 16 hrs.

EXAMPLE 16

A single-phase perovskite material Ln_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)O₃was synthesized according to the method described in Example 15. Theproduct was found to be a single-phase perovskite powder. The surfacearea varied depending on the precise heat treatment. The B.E.T. specificsurface area was 9.4 m²/g if the heat treatment was 1000° C. for 16 hrs.

This composition was tested for its three-way catalytic conversionactivity in a gas that closely simulates automobile exhaust. Thecatalyst was found to have reasonable three-way conversion activity overa range of redox potentials.

EXAMPLE 17

A single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Ru_(0.06)O₃ was synthesized accordingto the method described in Example 15. Appropriate quantities of thesalt ruthenium nitrosyl nitrate were used as the soluble rutheniumsource. The product was found to be a single-phase perovskite powder,the surface area varied depending on the precise heat treatment. TheB.E.T. specific surface area was 3.2 m²/g if the heat treatment was1100° C. for 16 hrs.

EXAMPLE 18

A single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Ru_(0.06)O₃ (Ln=low-Ce mixture of La,Ce, Pr and Nd) was synthesized by the method described in Example 15.The product from heat treatments in air was found to be a single-phaseperovskite powder. The surface area varied depending on the precise heattreatment.

This composition was tested for its three-way catalytic conversionactivity in a gas that closely simulates automobile exhaust. Thecatalyst was found to have good three-way conversion activity over arange of redox potentials. The hydrocarbon and CO conversions inreducing gases were found to be superior to that of the materialdescribed in Example 15. It is clear that the catalyst is an efficientthree-way converter over a wide redox window, and thus, it is verysuitable for use in a three-way catalytic converter for the conversionof toxic emissions in combustion engine exhausts.

EXAMPLE 19

A single-phase perovskite material LnMn_(0.5)Cu_(0.5)O₃ was synthesizedaccording to the method described in Example 15. The product was foundto be a single-phase perovskite powder. The surface area varieddepending on the precise heat treatment. The B.E.T. specific surfacearea was 7.4 m²/g if the heat treatment was 1000° C. for 16 hrs.

This composition was tested for its three-way catalytic conversionactivity in a gas that closely simulates automobile exhaust. Thecatalyst was found to have reasonable three-way conversion activity overa range of redox potentials.

EXAMPLE 20

A single-phase perovskite material LnMn_(0.8)Ni_(0.10)Cu_(0.10)O₃ wassynthesized according to the method described in Example 15. The productwas found to be a single phase perovskite powder. The surface areavaried depending on the precise heat treatment. The B.T.E. specificsurface area was 10.1 m²/g if the heat treatment was 1000° C. for 16hrs.

This composition was tested for its three-way catalytic conversionactivity in a gas that closely simulates automobile exhaust. Thecatalyst was found to have reasonable three-way conversion activity overa range of redox potentials.

EXAMPLE 21

In this example, a single-phase perovskite material was made into powderand deposited onto a commercially available support structure. Asingle-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Pd_(0.06)O₃ was synthesized bydissolving 100 g of mixed carbonate and 400 g of malic acid in asolution formed by dissolving 121.14 g of hydrated manganese nitrate,19.84 g of strontium nitrate, 29.76 g of 10.0 wt % Pd nitrosyl nitratesolution and 5.46 g of nickel nitrate hexahydrate and 2 liters of water.The solution was dried and heat-treated at 800° C. for 16 hrs. in air.The single-phase powder was then formed into a slurry with water and 5%Dispural, and coated onto a 400 cells-per-square-inch cordieritehoneycomb. After drying, the coated honeycomb was heat-treated at 700°C. for 2 hrs. The loading of perovskite was in the rang,e 5-25 g perliter of geometric volume of substrate. The three-way performance atstoichiometric air-fuel ratios at 400° C. is given by 83.4% NOx, 92.1%CO and 85.2% THE.

EXAMPLE 22

In this example, a single-phase perovskite material in powder form wasmixed with a carrier powder. A single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Pd_(0.06)O₃ was synthesized bydissolving 100 g of mixed hydrated lanthanide carbonate and 400 g ofmalic acid in a solution formed by dissolving 121.14 g of hydratedmanganese nitrate. 19.84 g of strontium nitrate, 29.76 g of 10.0 wt % Pdnitrosyl nitrate solution and 5.46 g of nickel nitrate hexahydrate and 2liters of water. The solution was dried and heat-treated at 800° C. for16 hrs. in air. The single-phase powder was then formed into a slurry bymethods well known in the art, being mixed and milled with water,gamma-alumina, ceria-zirconia (Ce_(1-x)Zr_(x)O₂) and Dispural, andcoated onto a 300 cells-per-square-inch metal honeycomb substrate. Theratio of the four solid ingredients in the slurry is being given by:perovskite/alumina/ceria-zirconia/dispural=8/70/20/2 wt %. After drying,the coated honeycomb was heat-treated at 700° C. for 2 hrs. The loadingof solids per liter of honeycomb was in the range 70-200 g. Thethree-way performance in perturbed exhaust gas streams, space velocity80,000 hr⁻¹, with stoichiometric average air-fuel ratios at 400° C.after high temperature aging is given by 87.4% NOx, 95.1% CO and 88.2%THE.

EXAMPLE 23

In this example, a carrier powder was used to support an efficientlow-cost catalyst. A solution with the cation compositionLn_(0.7)Sr_(0.3)Mn_(0.9)Pd_(0.1) was synthesized according to theprevious example. This solution was then impregnated into agamma-alumina powder previously treated with bastnasite-derived mixedlanthanide nitrate solution and so having the formulaLn_(0.1)Al_(0.9)O₃. The powder at incipient wetness was then dried at85° C. for 5 hrs. and heated at 200° C. for 5 hrs, and then finally at900° C. for 16 hrs. The mixed powder contained 6 wt % perovskite andpossessed a high specific surface area even when heat-treated at 1100°C. for 20 hrs. The powder was then loaded onto a cordierite honeycombstructure by first forming, it into a slurry with 4% Dispural and waterand acetic acid. The coated honeycombs were loaded to 120 g/L with thecomposite powder.

The temperature known, as the light-off temperature—the temperatureabove which the catalyst is functioning—was measured for NOx, CO andhydrocarbons as 315° C., 225° C. and 234° C. respectively, for a 100,000hr⁻¹ space velocity.

EXAMPLE 24

In this example, pre-formed washcoats containing, one or more of thecarrier powders were used to support an efficient low-cost catalyst. Awashcoat was formed onto a cordierite honeycomb support with 600cells-per-square-inch consisting of ceria-zirconia (25% zirconia) andgamma alumina in the weight ratio of 1:5. The washcoat loading was inthe range 50-250 g per liter. A solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.9)Pd_(0.1) (containing 100 g malic acid per literof solution) was impregnated into the washcoated honeycombs and thechannels blown clear of excess. The parts were dried and heat-treated attemperatures in the range of 500-1000° C. The perovskite catalystloading was in the 2-12 g/L range in the final part.

The catalysts were aged according to a 4-mode accelerated aging cyclesimulating 100,000 miles of driving) a car. The emissions from thetailpipe of a 4-cylinder gasoline powered automobile were 0.06 g/milehydrocarbons, 1.3 g/mile CO and 0.12 g/mile NOx. These emissionscorrespond to reductions compared to those from the tailpipe of 95% HC,83% CO and 96% NOx over the Federal Test Procedure drive cycle.

EXAMPLE 25

In this example, a pre-formed washcoat containing fully formedperovskite pleases of the present invention was used to support anefficient low-cost catalyst. A washcoat was formed onto a cordieritehoneycomb support with 400 cells-per-square-inch consisting ofceria-zirconia (25% /zirconia) and gamma alumina in the weight ratio of1:5: but also containing 10 wt % perovskite of formulaLn_(0.8)Sr_(0.2)MnO₃. The washcoat loading was in the range 50-150 g perliter. A solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.98)Pd_(0.02) (containing 100 g malic acid perliter of solution) was impregnated into the washcoated honeycombs andthe channels blown clear of excess. The parts were dried andheat-treated at temperatures in the range of 600-900° C. The perovskitecatalyst Ln_(0.5)Sr_(0.5)Mn_(0.98)Pd_(0.02)O₃ was loaded in the 5-20g/L, range in

The catalysts were aged according to a 2-mode accelerated aging cyclesimulating 50,000 miles of driving a car and then tested on a benchreactor with simulated car exhaust. The transient conversionefficiencies of NOx, CO and HC, at 400° C. and 100,000 hr⁻¹ spacevelocity, were measured as 78%, 88% and 93%, respectively.

EXAMPLE 26

In this example, a pre-formed washcoat was used as a carrier. A washcoatwas formed onto a cordierite honeycomb support with 400cells-per-square-inch consisting of ceria-zirconia and perovskite offormula Ln_(0.8)Sr_(0.2)MnO₃ in equal weight proportions. The washcoatloading was in the range 50-100 g per liter. A solution with the cationcomposition Ln_(0.8)Sr_(0.2)Mn_(0.96)Pd_(0.04) (containing 100 g malicacid per liter of solution) was impregnated into the washcoatedhoneycombs and the channels blown clear of excess. The parts were driedand heat-treated at temperatures in the range of 600-900° C. Theperovskite catalyst Ln_(0.8)Sr_(0.2)Mn_(0.96)Pd_(0.04)O₃ was loaded inthe 5-10 g/L range in the final part.

The catalysts were aged according to a 2-mode accelerated aging cyclesimulating 50,000 miles of driving a car and then tested on a benchreactor with simulated car exhaust. The transient conversionefficiencies of NOx, CO and HC, at 400° C. and 12,000 hr⁻¹ spacevelocity, were measured as 81%, 86% and 95%, respectively.

EXAMPLE 27

In this example, high surface area inert powders were used to support anefficient low-cost catalyst. A single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.04)Pd_(0.06)O₃ was synthesized bydissolving 100 g of mixed hydrated lanthanide carbonate and 400 g ofmalic acid in a solution formed by dissolving 121.14 g of hydratedmanganese nitrate, 19.84 g of strontium nitrate, 29.76 g of 10.0 wt % Pdnitrosyl nitrate solution and 5.46 g of nickel nitrate hexahydrate and 2liters of water. The solution was dried and heat-treated at 800° C. for16 hrs. in air. The single-phase powder was then formed into a slurry bymethods well known in the art, being mixed and milled with water,gamma-alumina, ceria-zirconia (Ce_(1-x)Zr_(x)O₂) and Dispural, andcoated onto a 300 cells-per-square-inch metal honeycomb substrate. Theratio of the four solid ingredients in the slurry is being given by:perovskite/alumina/ceria-zirconia/dispural=8/70/20/2 wt %. After drying,the coated honeycomb was heat-treated at 700° C. for 2 hrs. The loadingof solids per liter of honeycomb was in the range 70-200 g. Thethree-way performance in perturbed exhaust gas streams, space velocity80,000 hr⁻¹ with stoichiometric average air-fuel ratios at 400° C. afterhigh temperature aging, is given by 87.4% NOx, 95.1% CO and 88.2% THC.

EXAMPLE 28

A washcoat was formed onto a cordierite honeycomb support with 600cells-per-square-inch consisting of ceria-zirconia (25% zirconia) andgamma alumina in the weight ratio of 1:5. The washcoat loading was inthe range 50-250 per liter. A solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.95)Pt_(0.05) (containing 100 g malic acid perliter of solution) was impregnated into the washcoated honeycombs andthe channels blown clear of excess. The parts were dried andheat-treated at temperatures in the range of 500-1000° C. The peroskitecatalyst loading, was in the 2-12 g/L range in the final part.

The catalysts were aged according to a 4-mode accelerated aging cyclesimulating 100,000 miles of driving a car. The emissions from thetailpipe of a 4-cylinder gasoline powered automobile were 0.06 g/milehydrocarbons, 1.3 g/mile CO and 0.12 g/mile NOx. These emissionscorrespond to reductions compared to those from the tailpipe of 95% HC,93% CO and 78% NOx over the Federal Test Procedure drive cycle.

EXAMPLE 29

A single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ni_(0.05)Pd_(0.03)O₃ was synthesized bydissolving the appropriate amounts of mixed hydrated lanthanidecarbonate, malic acid, hydrated manganese nitrate, strontium nitrate, Pdnitrosyl nitrate solution and nickel nitrate hexahydrate and 2 liters ofwater. The solution was dried and heat-treated at 800° C. for 16 hrs. inair. The single-phase powder was then formed into a slurry with waterand 5% Dispural, and coated onto a 400 cells-per-square-inch cordieritehoneycomb. After drying, the coated honeycomb was heat-treated at 700°C. for 2 hrs. The loading of perovskite was in the range 15-25 g perliter of (geometric volume of substrate. With a loading of 21 g/L, thethree-way performance at stoichiometric air-fuel ratios at 400° C. isgiven by 80.4% NOx, 91.1% CO and 84.2% THE.

EXAMPLE 30

A solution of cation compositionLn_(0.8)Sr_(0.2)Mn_(0.94)Pt_(0.05)Rh_(0.01)O_(3+d), was formed using thesalts mentioned in the previous example, in addition to DPN and rhodiumchloride. The solution was impregnated into a washcoat consisting ofceria-zirconia (25% zirconia) and gamma alumina in the weight ratio of1:5. The washcoat was pre-formed onto a cordierite honeycomb supportwith 400 cells-per-square-inch with a loading of 125 g per liter. Theimpregnated part was dried at 150° C. and heat-treated at 650° C. for 5hrs. The loading of catalyst was measured as 4 g per liter of catalyst.The three-way performance in perturbed exhaust gas streams, spacevelocity 80,000 hr⁻¹, with stoichiometric average air-fuel ratios at400° C. after high temperature aging is given by 93.4% NOx, 94.1% CO and87.2% THC.

EXAMPLE 31

A washcoat was formed onto a cordierite honeycomb support with 600cells-per-square-inch consisting of ceria-zirconia (25% zirconia) andgamma alumina in the weight ratio of 1:5. The washcoat loading was inthe range 100-120 g per liter. A solution with the cation compositionLn_(0.8)Ba_(0.2)Mn_(0.94)Pd_(0.06) (containing 100 g malic acid perliter of solution) was impregnated into the washcoated honeycombs andthe channels blown clear of excess. The parts were dried andheat-treated at temperatures in the range of 700-750° C. The perovskitecatalyst loading was in the 4-6 g/L range in the final part.

The catalysts were aged according to a 4-mode accelerated aging cyclesimulating 50,000 miles of driving a car. The light-off temperaturesafter aging were measured to be 280° C. for HC, 274° C. for CO and 310°C. for NOx.

EXAMPLE 32

In this example, a solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.98)Rh_(0.02)O_(3+d) was synthesized. This solutionwas then impregnated into a gamma-alumina powder previously treated withbastnasite-derived mixed lanthanide nitrate solution and so having theformula Ln_(0.1)Al_(0.9)O₃. The powder at incipient wetness was thendried at 85° C. for 5 hrs. and heated at 200° C. for 5 hrs. and thenfinally at 900° C. for 16 hrs. The mixed powder contained 4 wt %perovskite and possessed a high specific surface area even whenheat-treated at 1100° C. for 20 hrs. The powder was then loaded onto acordierite honeycomb structure by first forming it into a slurry with 4%Dispural and water and acetic acid. The coated honeycombs were loaded to120 g/L with the composite powder.

The temperature known as the light-off temperature—the temperature abovewhich the catalyst is functioning—was measured for NOx, CO andhydrocarbons as 243° C., 264° C. and 274° C., respectively, for a100,000 hr⁻¹ space velocity.

EXAMPLE 33

In this example, a single-phase perovskite materialLn_(0.8)Sr_(0.2)Co_(0.9)Ru_(0.1)O₃ was synthesized by the methoddescribed in Example 9. The solution was dried and heat-treated at 800°C. for 16 hrs, in air. The single-phase powder was then formed into aslurry by methods well known in the art, being mixed and milled withwater, gamma-alumina, ceria-zirconia (Ce_(1-x)Zr_(x)O₂) and Dispural,and coated onto a 300 cells-per-square-inch metal honeycomb substrate.The ratio of the four solid ingredients in the slurry is being given by:perovskite/alumina/ceria-zirconia/dispural=20/56/20/4 wt %. Afterdrying, the coated honeycomb was heat-treated at 700° C. for 2 hrs. ,Theloading of solids per liter of honeycomb was in the range 70-200 g. Thethree-way performance in perturbed exhaust gas streams, space velocity40,000 hr⁻¹, with stoichiometric average air-fuel ratios at 550° C.after high temperature aging is given by 89.4% NOx. 93.1% CO and 90.2%THC.

EXAMPLE 34

In this example, a single-phase perovskite materialLn_(0.8)Sr_(0.2)Mn_(0.9)Ru_(0.1)O₃ was synthesized by the methoddescribed in Example 8. The solution was dried and heat-treated at 800°C. for 16 hrs. in air. The single-phase powder was then formed into aslurry by methods well known in the art, being mixed and milled withwater, gamma-alumina, ceria-zirconia (Ce_(1-x)Zr_(x)O₂) and Dispural,and coated onto a 300 cells-per-square-inch metal honeycomb substrate.The ratio of the four solid ingredients in the slurry is being given by:perovskite/alumina/ceria-zirconia/dispural=15/60/20/5 wt %. Afterdrying, the coated honeycomb was heat-treated at 750° C. for 2 hrs. Theloading of solids per liter of honeycomb was in the range 100-150 g. Thethree-way performance in perturbed exhaust gas streams, space velocity40,000 hr⁻¹, with stoichiometric average air-fuel ratios at 500° C.after high temperature aging is given by 91.4% NOx, 83.0% CO and 86.2%THC.

EXAMPLE 35

A washcoat was formed onto a cordierite honeycomb support with 600cells-per-square-inch consisting of ceria-zirconia (25% zirconia) andgamma alumina in the weight ratio of 1:5. The washcoat loading was inthe range 50-250 g per liter. A solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.95)Pd_(0.05) (containing 100 g malic acid perliter of solution) was impregnated into the washcoated honeycombs andthe channels blown clear of excess. The parts were dried andheat-treated at temperatures in the range of 600-1000° C. The perovskitecatalyst loading was in the 2-12 g/L, range in the final part. A secondsolution with the cation Composition Ln_(0.5)Sr_(0.5)Co_(0.95)Ru_(0.05)(containing 100 g malic acid per liter of solution) was impregnated intothe washcoated and solution-impregnated honeycombs and the channelsblown clear of excess. The parts were dried and heat-treated attemperatures in the range of 600-1000° C. The second perovskite catalystloading was in the 4-10 g/L, range in the final part.

The catalysts were aged according to a 4-mode accelerated aging cyclesimulating 50,000 miles of driving a car. The emissions from thetailpipe of a 4-cylinder gasoline powered automobile were 0.09 g/milehydrocarbons, 1.6 g/mile CO and 0.09 g/mile NOx.

This catalyst also displayed good poison resistance to sulfur,maintaining stoichiometric and rich-of-stoichiometric NOx conversionefficiency in excess of 99% at 500° C.

EXAMPLE 36

This example shows that a non-perovskite-type catalyst may beimpregnated into a washcoat containing a perovskite-type catalyst. Inthis example, a non-perovskite-type catalyst of formula Sr₂Pd_(0.1)O_(x)is impregnated into a pre-formed carrier coating comprising aperovskite-type material Ln_(0.5)Sr_(0.5)MnO₃. The carrier coating alsocontains Ce_(0.75)Zr_(0.25)O₂ and gamma-alumina The ratio of the threeconstituents of the coating is 20 wt % Ln_(0.5)Sr_(0.5)MnO₃, 20 wt %Ce_(0.75)Zr_(0.25)O₂ and 60 wt % gamma-alumina. The carrier coating isformed onto a ceramic honeycomb with a cell density of 400cells-per-square-inch at a loading of 120 g per liter of substrate bythe slurry-coating technique well known in the art. A nitrate solutionwith the cation composition Sr₂Pd_(0.1) is formed from the appropriatenitrate precursors and water. The catalyst solution is then impregnatedinto the coated honeycomb, dried and calcined at 800° C. for 2 hrs. ThePd concentration in the heat-treated catalyst is 0.2 g per liter. Thethree-way performance at stoichiometric air-fuel ratios at 400° C. afteraging at 950° C. for 90 hrs. is given by 90.4% NOx 98.2% CO and 96.3%THC.

EXAMPLE 37

A washcoat was formed onto a cordierite honeycomb support with300-cells-per-square-inch consisting, of ceria-zirconia (25% zirconia)and gamma alumina in the weight ratio of 1:5. The washcoat loading ,wasin the range 120-140 g per liter. A solution with the cation compositionLn_(0.5)Sr_(0.5)Mn_(0.95)Pd_(0.05) (containing, 100 g malic acid perliter of solution) was impregnated into the washcoated honeycombs andthe channels blown clear of excess. The parts were dried andheat-treated at temperatures in the range of 700-900° C. The perovskitecatalyst loading was in the 4-6 g/L range in the final part. A secondsolution with the cation composition Ln_(0.5)Sr_(0.5)Mn_(0.95)Ru_(0.05)(containing 100 g malic acid per liter of solution) was impregnated intothe washcoated and solution-impregnated honeycomb and the channels blownclear of excess. The parts were dried and heat-treated at temperaturesin the range of 700-800° C. The second perovskite catalyst loading wasin the 3-4 g/L range in the final part.

The catalysts were aged according to a 2-mode, fuel-cut, acceleratedaging cycle simulating 50,000 miles of driving a car. The three-wayconversion efficiency at typical operating temperatures was measured as98.1% hydrocarbons, 91.2% CO and 96.7% NOx.

This catalyst also displayed good poison resistance to sulfur,maintaining stoichiometric and rich-of-stoichiometric NOx conversionefficiency in excess of 95% at 500° C.

THREE-WAY CATALYTIC ACTIVITIES OF PEROVSKITE MATERIALS OF THE PRESENTINVENTION EXAMPLE 38

Perovskite-type materials made according to the present invention aremeasured for their three-way catalytic activities. FIG. 3 shows theconversion percentages, catalyzed by a peroskite material of compositionLn_(0.8)K_(0.2)Mn_(0.95)Ru_(0.05)O₃ as described in Example 9, for theconversion of NO, HC and CO from a gas mixture simulating automobileexhausts with varying oxygen content. The space velocity of the gas was33,000 h⁻¹ and the temperature of the perovskite catalyst bed was heldat a temperature of 550° C. The redox potential of the (gas, R, isapproximated by {3C_(HC)+C_(co)}/{C_(NO)+2C_(O2)), wherein C representsthe concentration of the gases. In general, when R>1, the gas isclassified as a reducing gas which is generated by a fuel-rich exhaust.When R<1, the gas is classified as an oxidizing gas which is generatedby fuel-lean exhaust. In addition to these four gases, namely CO, C₃H₆,NO and O₂, carbon dioxide and steam were also present in the gasmixture.

For a gas mixture which is typical of engine exhaust from the middle ofthe range of air-fuel ratios (R=1.02), the material shows good three-wayconversion. Conversions of CO, NO and HC were 83.1,94.4 and 99.6,respectively. With fuel-rich gases (R=1.086, R=1.17) the material alsodisplayed excellent three-way conversion. This is unusual and is aunique feature of the mixed-valence oxide materials, and is also relatedto the Ce on the A-site for fuel-rich gases. The conversion of COdropped fractionally below 80%, the conversion of the HC was above 90%and the conversion of NO approached 100% (the output NO level wasmeasured less than 10 ppb). For gases simulating lean fuel-air mixtures(R=0.86), the NO conversion was below 10%. The CO conversion was above90% and the HC conversion was above 50%. The low conversion of NO inoxidizing gases is well known and is a direct consequence of thefundamental nature of the NO reduction process and the redox potentialof this gas.

The whole data set was highly reproducible; the gas mixture could becycled between “rich” (R=1.17) and “lean” (R=0.86) with repeatableconversions for all three critical gases. In addition, the conversionperformance for a particular gas (a given R) was not a function of thehistory of the sample testing, e.g., which type of gas was run first,etc., this s significant since a lot of the previous work on these typesof materials were plagued by hysterisis effects. Such effects wouldpreclude any realistic application of these materials in technologicalapplications.

In conclusion, FIG. 3 shows that the material made according to thepresent invention is active as a “three-way catalyst” with particularlyeffective performance at the rich end of the operating window (commonlyused in closed-loop, three-way catalytic converters). This superior richperformance is attributed to the presence of a mixed lanthanide A-sitein the perovskite; in particular, it can be attributed to the presenceof Ce on the A-site of the perovskite phase. It is understood that thematerials made according to the present invention contain at least about4% of CeO₂ on a LnO basis.

EXAMPLE 39

The temperature at which catalytic converter materials become active isvery important technologically and is commonly referred to as the“light-off” temperature. The catalytic activity of the material ismonitored as the catalyst bed is progressively heated up from ambienttemperatures.

FIG. 4 shows the light-off behavior of the material for a reducing gasmixture (R=1.17) with a space velocity of 61.300 h⁻¹. At temperaturesbelow 300° C. the material showed no conversion activity. In thetemperature window of 300° C. to 400° C., there was a rapid increase ofconversion activity with temperature. At 500° C. and above, conversionactivities for NO and HC were high (greater than 99.9% and 97.0%,respectively). This high activity was maintained up to the maximumtesting temperature of 900° C. The CO conversion activities wereslightly lower than the levels measured in the previous test (FIG. 3:conversion of CO at T=550° C. and R=1.17 was measured at 82.1%, whereasthe corresponding conversion in this test, FIG. 4 is approximately 75%).There is a significant decrease in CO conversion activity astemperatures are increased above 500° C. One possible cause of thisdecrease in CO conversion activity is the relatively high space velocityused in these measurements compared to that used in the earliermeasurements (61,300 h⁻¹ vs. 33,000 h⁻¹).

In conclusion, FIG. 4 shows that (1) the catalytic activity of thematerial is good at high temperatures (900° C.), and (2) there isappreciable activity significantly below the usual operating temperaturerange for a traditional catalytic converter (500° C.-700° C.). In otherwords, the material shows a considerable cold-start function.

EXAMPLE 40

The composition of Example 15 was tested for its three-way catalyticconversion activity in a gas that closely simulates automobile exhaust.FIG. 5 shows the three-way activity for 0.5 g (occupying about 1 cc involume) of the above perovskite composition in an exhaust gas flow rateof approximately 1 liter/min. The gas composition was 150 cc/min steam,210 cc/min carbon dioxide, 13.5 cc/min CO, 1.5 cc/min NO, 0.75 cc/minpropene and variable oxygen content. The oxygen content was varied toexplore the conversion efficiency over a wide range of redox potential,R. The bed temperature was 550° C.

It is clear that the catalyst is an efficient three-way converter over awide redox window. Therefore, it is very suitable for use in a three-waycatalytic converter for the conversion of toxic emissions in combustionengine exhausts.

EXAMPLE 41

This composition of Example 17 was tested for its three-way catalyticconversion activity in a gas that closely simulates automobile exhaust.FIG. 6 shows the three-way activity for 0.5 g (occupying about 1 cc involume) of the above perovskite composition in an exhaust gas flow rateof approximately 1 liter/min. The gas composition was 150 cc/mim steam,210 cc/mim carbon dioxide, 13.5 cc/min CO, 1.5 cc/min NO, 0.75 cc/minpropene and variable oxygen content. The oxygen content was varied toexplore the conversion efficiency over a wide range of redox potential,R. The bed temperature was 550° C. The catalyst was found to have goodthree-way conversion activity over a range of redox potentials. It isclear that the catalyst is an efficient three-way converter over a wideredox window, and thus, it is very suitable for use in a three-waycatalytic converter for the conversion of toxic emissions in combustionengine exhausts.

The excellent thermal stability of this composition was shown by x-raydiffraction (XRD) on powder samples before and after treatment in thereducing exhaust gas at 1000° C. for 5 hrs. There was no noticeabledecomposition of the perovskite phase to reduced perovskite phases ordecomposition of the perovskite phase altogether.

The present invention may be embodied in other specific forms withoutdeparting from its essential characteristics. The described embodimentis to be considered in all respects only as illustrative and not asrestrictive. The scope of the present invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of the equivalence ofthe claims arc to be embraced within their scope.

What is claimed is:
 1. A perovskite-type catalyst consisting essentiallyof a metal oxide composition represented by the general formula:A_(1−x)B_(x)MO₃ wherein A is a mixture of elements originally in theform of a single phase mixed lanthanide collected from bastnasite; B isa divalent or monovalent cation; M is at least one element selected fromthe group consisting of elements of an atomic number of from 22 to 30,40 to 51, and 73 to 80; and x is a number defined by 0≦x<0.5, whereinthe perovskite-type catalyst selected from the group consisting ofLn_(0.5)Sr_(0.5)Mn_(0.95)Pt_(0.05)O₃;Ln_(0.8)Sr_(0.2)Mn_(0.92)Ni_(0.05)Pd_(0.03)O₃;Ln_(0.8)Sr_(0.2)Mn_(0.94)Pt_(0.05)Rh_(0.01)O₃;Ln_(0.8)Ba_(0.2)Mn_(0.94)Pd_(0.06) ₃;Ln_(0.5)Sr_(0.5)Mn_(0.98)Rh_(0.02)O₃;Ln_(0.8)Sr_(0.2)Co_(0.9)Ru_(0.1)O₃; Ln_(0.8)Sr_(0.2)Mn_(0.9)Ru_(0.1)O₃;Ln_(0.7)Sr_(0.3)Mn_(0.9)Pd_(0.1)O₃; Ln_(0.5)Sr_(0.5)Mn_(0.9)Pd_(0.1)O₃;Ln_(0.5)Sr_(0.5)Mn_(0.98)Pd_(0.02)O₃, and Ln_(0.8)Sr_(0.2)MnO₃.
 2. Aperovskite-type catalyst of claim 1 having a formulaLn_(0.05)Sr_(0.5)Mn_(0.95)Pt_(0.95)O₃.
 3. A perovskite-type catalyst ofclaim 1 having a formula Ln_(0.8)Sr_(0.2)Mn_(0.92)Ni_(0.05)Pd_(0.03)O₃.4. A perovskite-type catalyst of claim 1 having, a formulaLn_(0.8)Sr_(0.2)Mn_(0.94)Pt_(0.05)Rh_(0.01)O₃.
 5. A perovskite-typecatalyst of claim 1 having a formulaLn_(0.8)Ba_(0.2)Mn_(0.94)Pd_(0.06)O₃.
 6. A perovskite-type catalyst ofclaim 1 having a formula Ln_(0.5)Sr_(0.5)Mn_(0.98)Rh_(0.02)O₃.
 7. Aperovskite-type catalyst of claim 1 having a formulaLn_(0.8)Sr_(0.2)Co_(0.9)Ru_(0.1)O₃.
 8. A perovskite-type catalyst ofclaim 1 having a formula Ln_(0.8)Sr_(0.2)Mn_(0.9)Ru_(0.1)O₃.
 9. Aperovskite-type catalyst of claim 1 having a formulaLn_(0.7)Sr_(0.3)Mn_(0.9)Pd_(0.1)O₃.
 10. A perovskite-type catalyst ofclaim 1 having a formula Ln_(0.5)Sr_(0.5)Mn_(0.9)Pd_(0.1)O₃.
 11. Aperovskite-type catalyst of claim 1 having a formulaLn_(0.5)Sr_(0.5)Mn_(0.98)Pd_(0.02)O₃.
 12. A perovskite-type catalyst ofclaim 1 having a formula Ln_(0.8)Sr_(0.2)MnO₃.